The motion of electrons within a single isolated atom or molecule generates electromagnetic fields which can be detected external to the boundaries of the atom or molecule. The magnitude and frequency of such external fields depends mainly upon the following factors:
(i) the angular momentum of the electron as it spins on its axis (=electron spin angular momentum), PA1 (ii) the angular momentum of the electron as it moves in quasicircular orbital paths around the nucleus (=electron orbital momentum), PA1 (iii) the quantized energy states of the electron orbital paths and angular spin velocities, PA1 (iv) intraatomic and intramolecular interactions between electron motions as governed by Lenz's law, PA1 (v) rate of individual transitions between quantized energy states and the frequency of transitional events, PA1 (vi) interactions between electron orbital and spin angular moments and nuclear magnetic moments, and PA1 (vii) intensity, frequency and direction of externally imposed magnetic fields.
The electromagnetic fields generated by electron motion within atoms or molecules are accompanied by the simultaneous emission of photons whose energies are characteristic of the frequencies of the associated atomically- or molecularly-generated external magnetic fields. The range of atomic and molecular electromagnetic frequencies extends from microwave to ultraviolet energies.